It is known that the presence of people in a specific detection area inside a room can be detected by means of various motion detectors with electro-magnetic radiation and sound waves, and to control a connected external electrical device by means of the detection. Generally in this case, the switching on lighting or cameras is known which are combined with a motion detector and which are activated as soon as the detector identifies an object inside the monitoring area, commonly defined as event. However, more complex systems are controlled using motion detection, e.g. control of robots within automatic plants without colliding. Conditions for this are that following the motion detection an output signal is generated which can be used for controlling the connected device. As the output signal is normally of an electrical nature where necessary by means of different transformations, the to be controlled external device using such signal shall in the following be defined as an electrical device.
Wherein active motion detectors have an artificial source that produces electro-magnetic radiation and sound waves to detect changes of the current situation inside the detection area, passive motion detectors use sound waves that are present with or without the presence of a person inside the detection area.
Passive detectors can be in particular infrared motion detectors which operate with far-infrared detector, and which uses the heat that a person inside the detection area radiates. The change of radiation of heat that is associated with the movement of a person induces an electrical signal in the sensor of the motion detector which by a suitable preparation of the signal for the use in a subsequent circuit stage is often provided to the actuator of a control circuit such as for switching and dimming of lights which is dependent on the brightness of the surrounding.
Passive motion detectors are also so called Reichardt-Detectors that detect changes of the light in the surrounding. In this case, movements are locally resolved, i.e. the direction of a movement is detected by delaying and linking signals to one another from several at least two adjacent detectors. Such a motion detector is called EMD-Sensor (Elementary Motion Detector; EMD).
Through the use of several EMDs, a directional and speed specific signal is to be sustained, and a complete half-space is to be covered through a suitable arrangement of an EMD within an EMD array. For instance through that, the speed, also angular speed, as well as the direction of movement of an object approaching a vehicle are determined in vehicle assistance systems.
For active motion detectors, various signals are used of whose reflection at an object, the presence of the object in the monitoring area or its movement as well as various other values are identified. There are known motion detectors that can determine distance, speed and acceleration of an object by the use of ultrasound pulses which are emitted from the detector that make use of the Doppler principle by measuring the time delay.
A three-dimensional object recognition, which also comprises information on the distance to the object, often takes place using stereoscopic cameras or scanning systems which however are very complex and costly. Also, objects can be displayed in a three-dimensional way by measuring the time delay of the radiation that is emitted from a pulsed radiating source.
Time delay measurements are realized using methods of measuring pulses or by determination of modulated light from phase shifting. Whereas for the method to measure pulses, time delays between the light pulses are evaluated which are reflected at an object or not, continuously emitted light and changes in the light as a consequence of a reflection at an object is used as a basis of the evaluation of the phase shift.
Detection systems operate continuously, or by manual or automatic initiation through a superordinate main system so that the integration of distance or motion detectors in an operating system such as a driver-assistance system in regards to the operational readiness can take place without any problems. If however the superordinate or main system is deactivated, where need be storage of energy is required to keep the detection system in standby. Because, immobilization times of vehicles can be very long, having the detection systems on standby does not strain the battery too much. But also for the detection operations, the power input shall be reduced because there are a high amount of users in the main system and because of demands for improved energy efficiency.